Renewable energy and materials is a rapidly growing field, the development of which is in higher demand than ever. One major branch of renewable energy is organic electronics and semiconducting materials. Organic semiconductors have several advantages over their silicon-based counterparts including renewability, their ability to be solution-processed into lightweight and flexible films, and their ability to have their properties easily tuned through chemical synthesis.
Important progress has been made towards making organic semiconductor technology ubiquitous in everyday uses. Technologies such as organic photovoltaics (OPVs) and organic batteries may provide a practical path to achieve low-cost, renewable energy harvesting, and storage. Plastic polymeric power generation and storage sources offer intriguing opportunities for both portable solar cells and batteries, as such materials are potentially flexible, lightweight, and easy to fabricate through low-cost processing techniques. Further, organic molecules may offer malleable properties that are easy to tune through chemical synthesis.
Typically, organic semiconducting materials (OSMs) are only soluble in organic solvents, and sometimes this solubility may be limited. This low solubility is mostly due to OSM designs having a highly planar nature that allows for optimal overlap of their pi-electron clouds and a high degree of crystallinity. The problem of solubility is typically dealt with by affixing alkyl side chains to the aromatic molecules that make up the polymer (or small molecule) backbone. Finding the appropriate side chain is unique to each new donor-acceptor polymer system that is designed, and certain chains lengths and chain branching works better for some systems than others. This delicate balance between solubility and planarity can make for long and arduous molecular designing to obtain the ideal material.
The vast majority of polymers that have been successfully used in OPVs are comprised of an alternating electron-rich (donor) and electron-deficient (acceptor) co-monomers, called donor-acceptor (D-A) copolymers. Typically, it is much easier, for synthetic reasons, to affix alkyl chains to the donor molecules. For this reason, the library of known donor molecules is much more diverse than that of the acceptor molecules. There exists a need for acceptors that can also positively affect solubility.